Doctor: Peter Capaldi (Twelfth Doctor)
Companion: Jenna Coleman (Clara Oswald)
Samuel Anderson – Danny Pink
John Cummins – Roscoe
Jessica Hayles – PC Forrest
Joivan Wade – Rigsy
Christopher Fairbank – Fenton
Matt Bardock – Al
Raj Bajaj – George
James Quinn – Bill
Michelle Gomez – Missy
Directed by Douglas Mackinnon
Written by Jamie Mathieson
Script editor David P Davis
Produced by Nikki Wilson
Executive producer(s) Steven Moffat
Incidental music composer Murray Gold
Series Series 8
Length 45 minutes
Originally broadcast 18 October 2014
On returning Clara Oswald to London, the Doctor finds that something is draining energy from the TARDIS and they end up in Bristol instead. They find the TARDIS' exterior size has shrunk as a result of the energy drain, and the Doctor sends Clara out to learn more while he tries to stop the drainage. Clara befriends Rigsy, a graffiti artist now performing community service with a small crew. Rigsy informs her that several people have gone missing recently, their disappearances depicted on a mural in a pedestrian tunnel painted by an unknown person. Clara returns to find that the TARDIS has now shrunk so much that the Doctor cannot come out of its door. He passes her his sonic screwdriver, psychic paper, and an earpiece to let her communicate with him and see what she sees, and asks her to carry the TARDIS with her as she rejoins Rigsy, taking on the role of "Doctor Oswald" and adopting several of the Doctor's mannerisms.
At the flat of the latest disappearance they find nothing amiss save for a strange mural of a desert on one wall. With the help of police constable Forrest, they enter the flat of the first disappearance, and the Doctor instructs them to tear out a wall as he suspects that the source is within. In the next room, PC Forrest is suddenly absorbed into the floor, and by the time Clara and Rigsy arrive, she is gone. The Doctor finally realises that the murals are in the shape of a human nervous system and of a piece of human skin and that the attacks come from creatures, which he nicknames Boneless, that live in two dimensions and are experimenting to understand the third dimension. Clara and Rigsy manage to escape through a window using a hanging chair. During the escape, Danny Pink calls Clara as she is late for their meeting in London. The Doctor overhears the call and knows that Clara has lied, both to Danny about the nature of her travels with the Doctor, and to the Doctor in affirming Danny's acceptance of her traveling with the Doctor.
Clara and Rigsy race to stop the community workers from painting over the murals in the tunnel, which the Doctor has deduced are victims, but the creatures are hiding among them and they take one of the workers. Clara directs the rest to a nearby train maintenance yard and follows the Doctor's instructions to try to communicate with the creatures in the hope there may be a misunderstanding. The creatures however take another of the workers before the group flee into a disused tunnel, finding their escape routes blocked by flattened doors. Though the Doctor creates a device for Clara to restore the door's dimensions, the creatures have learned to project themselves in three-dimensions through shambling versions of their past victims and give chase. With the TARDIS losing further energy in the process, it spills out of Clara's handbag and falls onto an active train track; the Doctor activates the TARDIS's "siege mode" to protect it from harm from an oncoming train, but leaving it powerless to revert out or for the Doctor to communicate with Clara.
Clara is able to stop an out-of-service train and they use it to attempt to ram the creatures and give themselves time, but they simply transform it to a two-dimensional image. As they flee, Clara finds the TARDIS, now simply a cube, and takes it with her. In a disused office, Clara comes up with a plan, and has Rigsy paint a realistic-looking door on the back of a large poster which they then hang over an open doorway in a tunnel for the creatures to find on the assumption that it is a flattened door. When the Boneless attempt to unflatten the fake door, their energy ends up funneling power back to the TARDIS, which returns to its normal size while creating a barrier to hold the creatures in place. The Doctor, seeing that they have no interest in peace, returns the Boneless back to their dimension with a warning for those that survive the process never to return. Clara rejects a call from Danny, catching the Doctor's attention. He notes that she enjoyed "playing the Doctor" for the day.
The episode concludes with Missy, seated in a darkened room, watching Clara's adventure on a tablet computer. Missy says, with regard to Clara, that she has "chosen well".